1. 4GLS Cavity considerations for BBU Emma Wooldridge Accelerator Science and Technology Centre

2. ERL’07, 21 st to 25 th May 2007 Emma Wooldridge Ferrite Dampers Perturbed cavities Linac focusing

3. ERL’07, 21 st to 25 th May 2007 Emma Wooldridge Ferrite Dampers By including ferrite dampers near the cavity power can be removed from the Higher Order Modes Dampers are placed on each end of the cavity at 80K to minimise cryogenic load In a module dampers alternate diameter between larger and smaller

4. ERL’07, 21 st to 25 th May 2007 Emma Wooldridge Dampers continued Tiles are made from three different materials, each optimised to absorb HOMs at different frequencies. One good at low frequencies <10GHz (Ferrite TT2-111R) One good at middle and high frequencies >10GHz (Ferrite HexMZ) One good at higher frequencies >25GHz (Ceramic ZR20CB5)

5. ERL’07, 21 st to 25 th May 2007 Emma Wooldridge Effect of Dampers on the BBU threshold Basic model created with two loops of TT2-112R ferrite Increase in BBU threshold of around 30%

6. ERL’07, 21 st to 25 th May 2007 Emma Wooldridge Altering the Cavity Introduce small defects in each cell to split the degeneracy of dipole modes Early results suggest that alternating the perturbation in x then y produces significantly higher thresholds Further tests required Could this be errors in the model or a real effect?

7. ERL’07, 21 st to 25 th May 2007 Emma Wooldridge Linac Focusing Three linac focusing schemes designed with Singlet Doublet Triplet of quadrupoles between each module

8. ERL’07, 21 st to 25 th May 2007 Emma Wooldridge Linac Focusing Continued 1

9. ERL’07, 21 st to 25 th May 2007 Emma Wooldridge Linac Focusing Continued 2 Idealised recirculation used in all threshold calculations K value of the magnets scanned to find optimum value Tesla 9 – cell cavity HOMs used Will be updated as the 4GLS lattice design settles

10. ERL’07, 21 st to 25 th May 2007 Emma Wooldridge Future Work Investigate the HOM damper Model realistic damper and investigate effect on BBU threshold Verify cavity perturbation results